MAXILLARY CUSPIDS (CANINE)

The maxillary cuspid is usually the longest tooth in either jaw. canines are considered the corner stones of the dental arch They are the only teeth in the dentition with a single cusp.

Facial Surface:- The facial surface of the crown differs considerably from that of the maxillary central or lateral incisors. In that the incisal edges of the central and lateral incisor are nearly straight, the cuspid has a definite point, or cusp.  There are two cutting edges, the mesioincisal and the distoincisal. The distoincisal cutting edge is the longer of the two. The developmental grooves prominent on the facial surface  extending two-thirds of the distance from the tip of the cusp to the cervical line.  The distal cusp ridge is longer than the mesial cusp ridge

Lingual Surface:  Distinct mesial and distal marginal ridges, a well-devloped cingulum, and the cusp ridges form the boundries of the lingual surface. The prominent lingual ridge extends from the cusp tip to the cingulum, dividing the lingual surface into mesial and distal fossae.

Proximal: The mesial and distal aspects present a triangular outline. They resemble the incisors, but are more robust--especially in the cingulum region

Incisal: The asymmetry of this tooth is readily apparent from this aspect. It usually thicker labiolingually than it is mesiodistally. The tip of the cusp is displaced labially and mesial to the central long axis of this tooth.

Root Surface:-The root is single and is the longest root in the arch. It is usually twice the length of the crown.

MANDIBULAR CENTRAL INCISORS

These are the first permanent teeth to erupt, replacing deciduous teeth, and are the smallest teeth in either arch

Facial Surfaces:-The facial surface of the mandibular central incisor is widest at the incisal edge. Both the mesial and the distal surfaces join the incisal surface at almost a 90° angle. Although these two surfaces are nearly parallel at the incisal edge, they converge toward the cervical margin. The developmental grooves may or may not be present. When present, they appear as very faint furrows.

Lingual: The lingual surface has no definite marginal ridges. The surface is concave and the cingulum is minimal in size.

Proximal: Both mesial and distal surfaces present a triangular outline.

Incisal: The incisal edge is at right angles to a line passing labiolingually through the tooth reflecting its bilateral symmetry.

Root Surface:-The root is slender and extremely flattened on its mesial and distal surfaces.

Types of dentitions:

1. Diphyodont. Teeth develop and erupt into their jaws in two generations of teeth. The term literally means two generations of teeth.

2. Monophyodont. a single generation of teeth.

3. Polyphyodont. Teeth develop a lifetime of generations of successional teeth

4. Homodont. all of the teeth in the jaw are alike. They differ from each other only in size.

5. Heterodont. There is distinctive classes of teeth that are regionally specialized.

Histology of the Periodontal Ligament (PDL)

Embryogenesis of the periodontal ligament
The PDL forms from the dental follicle shortly after root development begins
The periodontal ligament is characterized by connective tissue. The thinnest portion is at the middle third of the root. Its width decreases with age. It is a tissue with a high turnover rate.

FUNCTIONS OF PERIODONTIUM

Tooth support
Shock absorber
Sensory (vibrations appreciated in the middle ear/reflex jaw opening)

The following cells can be identified in the periodontal ligament:
a) Osteoblasts and osteoclasts b) Fibroblasts,  c) Epithelial cells
 

Rests of Malassez
d) Macrophages
e) Undifferentiated cells
f) Cementoblasts and cementoclasts (only in pathologic conditions)
The following types of fibers are found in the PDL
-Collagen fibers: groups of fibers
-Oxytalan fibers: variant of elastic fibers, perpendicular to teeth, adjacent to capillaries
-Eluanin: variant of elastic fibers
Ground substance

PERIODONTAL LIGAMENT FIBERS

Principal fibers
These fibers connect the cementum to the alveolar crest. These are:

a. Alveolar crest group: below CE junction, downward, outward
b. Horizontal group: apical to ACG, right angle
c. Oblique group: numerous, coronally to bone, oblique direction
d. Apical group: around the apex, base of socket
e. Interradicular group: multirooted teeth

Gingival ligament fibers
This group is not strictly related to periodontium. These fibers are:

a. Dentogingival: numerous, cervical cementum to f/a gingiva
b. Alveologingival: bone to f/a gingiva
c. Circular: around neck of teeth, free gingiva
d. Dentoperiosteal: cementum to alv. process or vestibule (muscle)
 e. Transseptal: cementum between adjacent teeth, over the alveolar crest
 

Blood supply of the PDL
The PDL gets its blood supply from perforating arteries (from the cribriform plate of the bundle bone). The small capillaries derive from the superior & inferior alveolar arteries. The blood supply is rich because the PDL has a very high turnover as a tissue. The posterior supply is more prominent than the anterior. The mandibular is more prominent than the maxillary.

Nerve supply
The nerve supply originates from the inferior or the superior alveolar nerves. The fibers enter from the apical region and lateral socket walls. The apical region contains more nerve endings (except Upper Incisors)

Dentogingival junction

This area contains the gingival sulcus. The normal depth of the sulcus is 0.5 to 3.0 mm (mean: 1.8 mm). Depth > 3.0 mm is considered pathologic. The sulcus contains the crevicular fluid
 

 
The dentogingival junction is surfaced by:
1) Gingival epithelium: stratified squamous keratinized epithelium 2) Sulcular epithelium: stratified squamous non-keratinized epithelium The lack of keratinization is probably due to inflammation and due to high turnover of this epithelium.
3) Junctional epithelium: flattened epithelial cells with widened intercellular spaces. In the epithelium one identifies neutrophils and monocytes.
Connective tissue
The connective tissue of the dentogingival junction contains inflammatory cells, especially polymorphonuclear neutrophils. These cells migrate to the sulcular and junctional epithelium.
The connective tissue that supports the sulcular epithelium is also structurally and functionally different than the connective tissue that supports the junctional epithelium.

Histology of the Col (=depression)

The col is found in the interdental gingiva. It is surfaced by epithelium that is identical to junctional epithelium. It is an important area because of the accumulation of bacteria, food debris and plaque that can cause periodontal disease.
Blood supply: periosteal vessels
Nerve supply: periodontal nerve fibers, infraorbital, palatine, lingual, mental, buccal

Dentin

1. Composition

a. Inorganic (70%)—calcium hydroxyapatite crystals.

b. Organic (30%)—water and type I collagen.

2. Types of dentin

a. Primary dentin

(1) Dentin formed during tooth development, before completion of root formation.

It constitutes the majority of dentin found in a tooth.

(2) It consists of a normal organization of dentinal tubules.

(3) Circumpulpal dentin

(a) The layer of primary dentin that surrounds the pulp chamber.  It is formed after the mantle dentin.

(b) Its collagen fibers are parallel to the DEJ.

b. Secondary dentin

(1) Dentin formed after root formation is complete.

(2) Is deposited unevenly around the pulp chamber, forming along the layer of dentin closest to the pulp.

It therefore contributes to the decrease in the size of the pulp chamber as one ages.

(3) It consists of a normal, or slightly less regular, organization of dentinal tubules. However,

as compared to primary dentin, it is deposited at a slower rate.

(4) Although the dentinal tubules in secondary dentin can be continuous with those in primary

dentin, there is usually a tubular angle change between the two layers.

c. Tertiary (reparative, reactive) dentin

(1) Dentin that is formed in localized areas in response to trauma or other stimuli such as caries, tooth wear, or dental work.

(2) Its consistency and organization vary. It has no defined dentinal tubule pattern

d. Mantle dentin
 

(1) The outermost layer of dentin
(2) Is the first layer of dentin laid down by odontoblasts adjacent to the DEJ.

(3) Is slightly less mineralized than primary dentin.

(4) Has collagen fibers that are perpendicular to the DEJ.

(5) Dentinal tubules branch abundantly in this area.

e. Sclerotic (transparent) dentin

(1) Describes dentinal tubules that have become occluded with calcified material .

(2) Occurs when the odontoblastic processes retreat, filling the dentinal tubule with calcium phosphate crystals.

(3) Occurs with aging.

f. Dead tracts

(1) When odontoblasts die, they leave behind empty dentinal tubules, or dead tracts.

(2) Occurs with aging or trauma.

(3) Empty tubules are potential paths for bacterial invasion.

3. Structural characteristics and microscopic features:
 

a. Dentinal tubules

(1) Tubules extend from the DEJ to the pulp chamber.

(2) The tubules taper peripherally (i.e., their diameters are wider as they get closer to the pulp). Since the tubules are distanced farther apart at the periphery, the density of tubules is greater closer to the pulp.

(3) Each tubule contains an odontoblastic process or Tomes’ fiber.

Odontoblastic processes are characterized by the presence of a network of microtubules, with

Occasional mitochondria and vesicles present.

Note: the odontoblast’s cell body remains in the pulp chamber.
 

(4) Coronal tubules follow an S-shaped path, which may result from the crowding of  odontoblasts as they migrate toward the pulp during dentin formation.

b. Peritubular dentin (intratubular dentin)

(1) Is deposited on the walls of the dentinal tubule, which affects (i.e., narrows)the diameter of the tubule .

(2) It differs from intertubular dentin by lacking a collagenous fibrous matrix. It is also more mineralized than intertubular dentin.
 

c. Intertubular dentin

(1) The main part of dentin, which fills the space between dentinal tubules

 (2) Is mineralized and contains a collagenous matrix.

d. Interglobular dentin

(1) Areas of hypomineralized or unmineralized dentin caused by the failure of globules or calcospherites to fuse uniformly with mature dentin.

(2) Dentinal tubules are left undisturbed as they pass through interglobular dentin; however,

No peritubular dentin is present.

(3) Interglobular dentin is found in the:

(a) Crown—just beneath the mantle dentin.

(b) Root—beneath the dentinocemental junction, giving the root the appearance of a granular

layer (of Tomes).

e. Incremental lines

(1) Dentin is deposited at a daily rate of approximately 4 microns.

(2) As dentin is laid down, small differences in collagen fiber orientation result in the formation of incremental lines.

(3) Called imbrication lines of von Ebner.

(a) Every 5 days, or about every 20 µm, the changes in collagen fiber orientation appear more

accentuated. This results in a darker staining line, known as the imbrication line of von

Ebner.

(b) These lines are similar to the lines of Retzius seen in enamel.

f. Contour lines of Owen

(1) An optical phenomenon that occurs when the secondary curvatures of adjacent dentinal tubules coincide, resulting in the appearance of lines known as contour lines of Owen.
 

(2) Contour lines of Owen may also refer to lines that appear similar to those just described; however, these lines result from disturbances in mineralization.

g. Granular layer of Tomes

(1) A granular or spotty-appearing band that can be observed on the root surface adjacent to the dentinocemental junction, just beneath the cementum.

Pulp

1. Four zones—listed from dentin inward

a. Odontoblastic layer

(1) Contains the cell bodies of odontoblasts.

Note: their processes remain in dentinal tubules.

(2) Capillaries, nerve fibers, and dendritic cells may also be present.

b. Cell-free or cell-poor zone (zone of Weil)

(1) Contains capillaries and unmyelinated nerve fibers.

c. Cell-rich zone

(1) Consists mainly of fibroblasts. Macrophages, lymphocytes, and dendritic cells may also be present.

d. The pulp (pulp proper, central zone)

(1) The central mass of the pulp.

(2) Consists of loose connective tissue, larger vessels, and nerves. Also contains fibroblasts and pulpal cells.

2. Pulpal innervation

a. When pulpal nerves are stimulated, they can only transmit one signal pain.

b. There are no proprioceptors in the pulp.

c. Types of nerves:

(1) A-delta fibers

(a) Myelinated sensory nerve fibers.

(b) Stimulation results in the sensation of fast, sharp pain.

(c) Found in the coronal (odontoblastic) area of the pulp.

(2) C-fibers

(a) Unmyelinated sensory nerve fibers.

(b) Transmits information of noxious stimuli centrally.

(c) Stimulation results in pain that is slower, duller, and more diffuse in nature.

(d) Found in the central region of the pulp.

(3) Sympathetic fibers

(a) Found deeper within the pulp.

(b) Sympathetic stimulation results in vasoconstriction of vessels.